This invention relates to a thermosetting resin, a prepreg and a laminate obtained by using the same, and a multilayer printed circuit board excellent in heat resistance, electrical properties and fire retardance obtained by using such a prepreg and/or laminates.
Heretofore, as laminate materials for multilayer printed circuit boards, there have mainly been used phenol resins, epoxy resins and polyimide resins. Particularly in the case of a large-sized computer, higher density is desired and thus there are used polyimide series resins excellent in heat resistance and dimensional stability. But recently, with a fast operational treatment in large-sized computers, there are required printed circuit boards excellent in electrical properties in order to improve a signalling rate. Particularly, in order to shorten a signalling delay time and to lessen a circuit thickness, printed circuit boards with a low dielectric constant are required. As the low dielectric constant laminate materials, there are developed laminates made from tetrafluoroethylene resin (PTFE), polybutadiene resins, etc. Such laminates are disclosed, for example, in Proc. NEPCON (1981), pp. 160-169, and Japanese Patent Unexamined Publication No. 55-127426.
But PTFE laminates have many problems in that since the resin is thermoplastic and has a low glass transition temperature, the thermal expansion coefficient is large at high temperatures and the dimensional stability is insufficient. Partiularly when a large number of PTFE layers are laminated and bonded, there is anxiety in through-hole reliability. Thus, when applied to multilayer printed circuit boards, the same wiring density as the epoxy resin is employed and a merit of being a low dielectric constant material is scarcely shown. Further, since there is no suitable solvent for the PTFE, a bonding method by heat melting contact bonding is generally employed. But there is a defect in that the melting temperature is very high.
On the other hand, polybutadiene resins have a defect of flammability from a viewpoint of molecular structure. In order to impart flame retardancy to polybutadiene resins, it is necessary to add an addition type flame retardant such as decabromodiphenyl ether, triphenyl phosphate, etc., a reaction type flame retardant such as tribromophenyl methacrylate, tribromophenyl acrylate, etc. But there is a problem in that the electrical properties, heat resistance and dimensional stability inherent to the polybutadiene resins are damaged by such an addition.